This invention relates to a spool for winding yarns, preferably in thermoplastic material, which may be compressed axially in a controlled way and according to a set value. The spool according to this invention is particularly suited for winding yarns that have to undergo hot and wet treatments, for example dyeing operation in an autoclave.
For yarn winding and treating operations the use of axially compressible spools in plastic material is already known from U.S. Pat. No. 3,465,984 of Sept. 9, 1969. The spools, before yarn dyeing in an autoclave, are slid over tubular support elements in order to be adequately compressed; in this way greater compactness is imparted to the wound yarn and the space taken up is reduced, before treating the yarn with the dye bath.
The use of winding spools known at present, involves various problems still unresolved, or inadequately resolved, which prevent satisfactory treatment of the yarns. In particular, it has been found that the low dimensional stability of the spool during winding of the yarn causes unwanted elongation of the spool which results in the yarn being wound on irregularly.
Another problem resides in the pinching and breaking of the yarn layers close to the spool body at the compression of the spool, with consequent damage to one or more layers of the wound yarn; this not only entails waste of yarn and therefore particularly appreciable economic loss if the yarn is of high quality, it also prevents the yarn from being wound off the spool, after the treatment, using the so-called head-tail system.
A third serious problem associated with the known type of spools, resides in the impossibility of adequately controlling the compression degree and therefore the density of packing of the yarn. In effect, differences have been found in compression and, therefore, in the packing density of the yarn, not only in each spool, but also in different spools on the same support element or on different support elements in an autoclave.
The effect of all this is that in the dyeing plant the treatment liquids are irregularly dispersed throughout the yarn mass or, more generally, the treatment of the yarns is non-homogeneous, resulting in damage to the product and unstable characteristics of the yarn. Effectively, in the case of yarn dyeing, the colouring obtained is non-homogeneous since the varying degree of bundling or packing of the yarn creates preferential passages for the dyeing liquid.
Accordingly, the general object of this invention is to provide an axially compressible yarn-winding spool, capable of avoiding the problems described above.
In particular, a first object of this invention is to provide a compressible spool, which may be controlled to avoid pinching the thread during compression, providing at the same time, before compression, a sufficient structural rigidity and dimensional stability to allow regular winding of the yarn.
A further object of the invention is to provide a spool, as a previously defined, by means of which it is possible to obtain an uniform compression and consequently a constant packing density of the yarn, by controlling to the degree of compressibility of the spool and the packing of the yarn according to a pre-set value.